The main aim of this project is to understand how the multi-functional tissue inhibitor of metalloproteinases-1 (TIMP-1) affects mammary carcinogenesis when administered exogenously and when expressed endogenously. The possibility that high endogenous TIMP-1 expression contributes to malignant tumor behaviour is based on three previous findings in our laboratory. First, abundant TIMP-1 transcripts are observed in cancer cells at the expanding front of human breast carcinomas. Second, in vivo tumor growth is increased and the angiogenic stimulator, vascular endothelial growth factor (VEGF), is up-regulated in TIMP-1 transfected rat mammary carcinoma cells. Third, there is a strong correlation between TIMP-1 and VEGF expression levels in human breast carcinoma cells lines. We have developed transgenic mouse lines for studies of endogenous and exogenous TIMP-1. The MMTV promoter targets TIMP-1 expression to breast epithelial cells to study the effect of elevated endogenous TIMP-1 levels on mammary carcinogenesis. The albumin promoter targets the liver for the production of large amounts of biologically active transgenic TIMP-1, which is released into the systemic circulation. Sustained 3-4-fold elevation of circulating TIMP-1 permits long-term evaluation of exogenous TIMP-1 on mammary tumor development. This transgenic model may also be valuable for studies to examine if exogenous TIMP-1 has beneficial effects on a variety of other disease processes where MMP-mediated tissue destruction has been implicated, such as rheumatoid arthritis and diabetic retinopathy. Carcinogenesis studies showed that elevated levels of circulating TIMP-1 suppressed significantly the incidence, multiplicity, and neovascularization of palpable mammary carcinomas in the Alb/TIMP-1 mice. Ongoing efforts focus on early mammary lesions to define the mechanism by which exogenous TIMP-1 suppresses neoplastic development. Preliminary data indicate that TIMP-1 is not suppressing the development of hyperplastic nodules but is altering the morphology of microscopic carcinomas. The second aim of this project is to understand the mechanism by which TIMP-1 inhibits angiogenesis. At the cellular level, TIMP-1 inhibited migration and caused cytoskeletal changes of microvascular endothelial cells, which was visualized by phalloidin staining of F-actin filaments. cDNA microarray analysis of rTIMP-1 treated and untreated microvascular endothelial cells showed that TIMP-1 suppressed transcription of the mitogenic VEGF receptor, KDR, as well as angiopoietin-1, which stimulates endothelial sprouting through focal adhesion kinase. These findings may help elucidate the molecular mechanism(s) by which TIMP-1 inhibits angiogenesis.